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Updated: Apr 5, 2026

Identification and Quantification of Decomposition Mechanisms in Lithium-Ion Batteries; Input to Heat Flow Simulation for Modeling Thermal Runaway

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Room-temperature second sound in isotopically pure graphite.

Zhikun Xie^1,2,3,4, Yifan Zhang^1,2,3,4, Xin Huang⁵

¹State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics, Sun Yat-sen University, Guangzhou, China.

Nature Communications

|April 3, 2026

Summary

Scientists observed second sound, a wave-like heat transport, in graphite at room temperature. This breakthrough enhances thermal conductivity and opens new avenues for heat transport applications.

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Published on: August 2, 2019

Area of Science:

Condensed Matter Physics
Materials Science
Phononics

Background:

Second sound, a wave-like heat transport phenomenon, is typically observed only at cryogenic temperatures in solids.
Disorder and Umklapp scattering commonly suppress second sound at ambient temperatures.

Purpose of the Study:

To directly observe second sound in solid crystals at room temperature.
To investigate the potential of isotopic purification in enabling hydrodynamic phonon transport.

Main Methods:

Utilized transient thermal grating spectroscopy.
Employed isotopically purified graphite to minimize phonon scattering.

Main Results:

Successfully observed a distinct damped oscillatory signal, providing unambiguous evidence of second sound.
Demonstrated an enhancement in effective thermal conductivity by nearly 10% above the diffusive limit.
Distinguished second sound from diffusive and ballistic phonon transport regimes.

Conclusions:

Control of phonon-isotope scattering is a viable strategy for achieving hydrodynamic phonon transport at room temperature.
Phonon hydrodynamics is an accessible phenomenon in room-temperature crystals.
This finding offers new possibilities for fundamental studies and applications of wave-like heat transport.